This invention relates generally to electro discharge machining apparatuses and methods. More particularly, this invention relates to electro discharge machining apparatuses and methods for drilling holes in workpieces.
Electro discharge machining (EDM) is a process in which a cathodic electrode is positioned atop an electrically conducting workpiece, and a dielectric liquid is channeled therebetween. Electrical current passes between the electrode and the workpiece, and locally erodes the workpiece for forming desired features therein. In a typical application, the electrode may be used for drilling holes of any desired shape in the workpiece.
For example, many gas turbine engine components are machined with small holes therein for cooling air passing through. In particular, the electrode may be inclined relative to the engine components to drill the holes. Generally, a process for machining the holes may comprise three stages, such as a touch-in stage, a normal drilling stage and a breakthrough stage.
However, in conventional electro discharge machining processes, especially when the electrode is inclined relative to the workpiece, the touch-in stage and/or the breakthrough stage may be time-consuming because of inefficient flushing of the dielectric fluid and short-circuits between the electrode and the workpiece.
Additionally, since the touch-in stage and the breakthrough stage may not be controlled well in the conventional machining process, the quality of the holes may deteriorate, which can reduce the lifetime of turbine engine components and cause cracking risks thereto.
Therefore, there is a need for a new and improved electro discharge machining apparatus and method for machining workpieces.